ARKit始终将对象保持在屏幕角落

Question

我有一个简单的对象，应该位于屏幕的左上角或右上角

我在pointOfView中添加了SCNNode，它在屏幕中央显示了它，但我希望它在任何角落

我做了

    let ball = SCNSphere(radius: 0.05)
    let matirial = SCNMaterial()
    matirial.diffuse.contents = UIImage(named: "image")
    ball.materials = [matirial]

    let ballNode = SCNNode(geometry: ball)
    ballNode.position = self.sceneView.pointOfView?.worldFront ?? SCNVector3(0,0,0) // cameraPosition == center.worldTransform
    ballNode.name = "ballCounter"
    self.sceneView.pointOfView?.addChildNode(ballNode)

我尝试过unprojectPoint，但现在球完全消失了

let point = self.sceneView.unprojectPoint(SCNVector3(20, 20, self.sceneView.pointOfView!.worldFront.z))
print("point of unproject \(point)" )
let convertedPoints = point
ballNode.position = convertedPoints

感谢您的任何帮助